i can't download an app because they won't accept my password

I can't download an app because they won't accept my password. I've tried using my aptdaemon password as well as my ubuntu password, and they won;t accept either one. Even when I go to the trouble of trying to change my password,they won't accept the new one. I don't know how I am ever going to get an app. Thank you. Sincerely, Christine Fowler

I'm sure there are a lot of people with the same problem! The think is... how can we solve this stupid problem??? I want to update my Lop Top but I can't because it wont accept my password____what's up with this!!!!!!!!!!!!